The present invention is related to an inductive element and a method of manufacturing the inductive element which is used as an inductor device having a stacked layer structure, a common mode choke coil, or a transformer. Otherwise, this inductive element may be constituted in combination with other elements, or may be used in such a mode that this inductive element is assembled in a module.
As one example of conventional inductive elements, spiral-shaped coils are formed by using a photolithography method on both a front surface and a rear surface of a core substrate, while the core substrate is made of either resin or a composite material manufactured by mixing functional material powder with resin (see, for example, Japanese Patent No. 2714343 (Particularly, pages 3 to 4, FIGS. 3 and 5).
Also, as another prior art, a stacked layer ceramics chip inductor is typically known. That is, since plural layers of green seats having conductor patterns wound by ½-turn to ¾-turns are stacked and the stacked multilayers are cut to be sintered, helical-shaped coils are wound up along the stacking direction (see, for example, Japanese Patent Publication No. HEI-11-103229 (Particularly, pages 4 to 5, FIG. 2).
Furthermore, as another conventional inductive element, there is a winding type inductive element. This conventional winding type inductive element is manufactured by winding a wire on a bobbin in a helical shape, while this wire constitutes a winding (see, for instance, Japanese Patent Publication No. HEI-11-204352 (Particularly, page 3, FIG. 2).
Also, as this sort of inductive element, a composite material made of both ferrite powder and resin is employed as an insulating base (see, for example, Japanese patent Publication No. HEI-10-270255 (pages 3 to 5, FIGS 1 and 2) and Japanese Patent Publication No. HEI-11-154611 (pages 4 to 6, FIGS. 1 and 2).
The conventional inductive element using the above-described thin-film type coil can hardly obtain a high Q characteristic (Q-factor) in view of the own construction of this conventional inductive element. Also, since the spiral coils are formed on the same planes of the core substrate, very fine processing is highly required for the conductor patterns, so that higher inductance values can be hardly realized. Also, in order to form the spiral coils, the patterning operations are required at least two times by employing the photolithography method. Therefore, there is such a problem that a total number of manufacturing stages is increased.
Also, as to the above-described stacked layer type inductive element, since the internal conductors are stacked in the multilayer form by employing the printing method, both printing fluctuation and stacking fluctuation occur. In addition, since the stacked layer type inductive element is sintered, the inductance precision is lowered due to shrinkage of the element and shrinkage fluctuation while this element is sintered. Thus, such an inductive element having narrow tolerance can be hardly manufactured.
Furthermore, because the sintered conductor patterns form a coil, it is difficult to obtain a high Q-factor.
Also, as to the above-explained winding type inductive element, since the wires are wound on the respective bobbins one by one, this winding type inductive element can be hardly made compact, and the better productivity thereof cannot be achieved, so that such a winding type inductive element can be hardly manufactured at a lower cost.
To solve the above-described problems, it is proposed another type of inductive element in Japanese Patent Publication 2003-197427. That is, through holes are formed in the form of two columns in a first layer which is made of either resin or such a composite material manufactured by mixing functional material powder with resin. A helical-shaped coil is constituted by a conductor which communicates between through holes formed in the different columns on the upper and lower planes of the first layer.
With employment of such an inductive element structure, the conductor patterns can be realized by way of a step capable of forming patterns in high precision such as a photolithography method. In addition, since the conductor pattern is formed on the flat portion of the first layer (core substrate), the positioning precision of the conductor patterns can be improved, and there is less characteristic fluctuation which is caused by shifts of the patterns when the patterns are stacked in the multilayer form. As a result, the narrow tolerance as to the electric characteristic can be achieved. Also, in this inductive element, the helical coil is not constructed in the stacking stage, but the helical-shaped coil is constituted by forming the plain conductor patterns. As a result, the helical-shaped coil can be constituted within a short time. Thus, the devices having the narrow tolerance as to the electric characteristic can be produced with low cost.
However, in this inductive element described in the prior patent application, the through holes must be formed in the core substrate by using laser or the like. If a depth of this through hole is larger than, or equal to approximately 0.3 mm, then the following problem occurs. That is, such a through hole whose diameter is approximately 0.02 mm can be hardly formed. Moreover, the through holes having the uniform sectional areas along the penetration direction of the through holes, and the conductors can be hardly filled/formed. Also, there is another problem that such through holes having the well-matched shapes can be hardly formed.